Fracturing formations in wells



June 30, 1959 J. D. CHESNUT 2,892,405

FRACTURING FORMATIONS IN WELLS Filed Dec. 29, 1952 15 Sheets-Sheet 1INVENTOR.

JOHN DEWEY CHESNUT w. M Q

"ATTORNEY June 30, 1959 J. D. CHESNUT FRACTURING FORMATIONS IN WfiLLS 3Sheets-Sheet 2 Filed Dec. 29, 1952 INVENTOR.

ATTQElVEY June 30, 1959 CHESNUT 2,892,405

FRACTURING EORMATIONS IN WELLS Filed Dec. 29, i952 3 Sheets-Sheet 3INVENTOR. JOHN DEWEY CHESNUT Bug/M ATTOENEY United States Patent2,892,405 I FRACTURING FORMATIONS IN WELLS john Dewey Chesnut, NewportBeach, Calif., assignoi', by theme assignments, to Aerojet-Gener'alCorporation, I Cincinnati, Ohio, a corporation of Ohio ApplicationDecember 29, 1952, Serial No. 328,408

" 8 Claims. (Cl. 10'2-23) This invention relates to the treatment of oiland gas wells. More particularly, the invention relates to a method forincreasing the permeability of the oil producing zones so that anincrease in the rate of oil production can be obtained.

.Heretofore it has been the practice to attempt to increase theproductivity of oil and gas wells by any one of several methods, withvarying success. Among the established methods are: (1) shooting withnitroglycerine, (2) acidizing, and (3) formation fracturing by theapplication of hydraulic pressure to the formation.

Shooting with nitroglycerine is a dangerous method owing to the verygreat sensitivity of nitroglycerine to shock and/or temperature changes.The usual method of operation is to lower a charge of nitroglycerineinto the well in a container and to detonate the nitroglycerine while inthe container. The resulting explosion may enlarge the well bore at thearea of explosion and may result in some fracturing of the formation insome instances. On the other hand, the force of the explosion within thebore hole tends to compact the formation, thus reducing its permeabilityto the flow of oil. Nitro shooting also creates a considerable quantityof debris in the bore of the well, which debris must subsequentlyPatented June 30, 19 59 are desired characteristics can be made bysensitizing mono nitromethane (CH NO by adding a small percentage of anamine or mixture of amines sufliciently basic to form salts with a weakacid, either organic or inorganic. Specific examples of such sensitizersare aniline, diethylamine or morpholine. The percent of sensitizer to beused is not critical and can be varied from one percent by volume to :asmuch as forty percent by volume but is generally on the order of twopercent to three percent.

Such a sensitized nitromethane is disclosed and claimed in the copendingapplication of Edgar A. Laurence, Serial No. 605,747, filed July 18,1945, and assigned to the same assignee as the present application.

The sensitized mixture can be detonated by means of high velocitydetonators such as some commercial blast- I ing caps or Primacord(pentaerythritoltetranitrate).

be removed by bailing. This latter operation may con-- sume severalweeks of time at a cost of many thousands of dollars. In many instancesnitro shooting is ineffective in increasing the production from the wellor not sufficiently eifective to warrant the expense of the job.

Acidizing, by treatment of calcareous formations with hydrochloric acid,is very effective in limestone or other formations which are soluble inhydrochloric acid but is not eifective on sandstones or othernon-calcareous formations. Acidizing has an advantage over nitroshooting in that the acid can be forced, by pressure, into the oilproducing formation for a considerable distance, thus providing agreatly increased drainage area as well as an increase in permeability.

1 Formation fracturing, by the application of high hydraulic pressure tooil producing formations in order to crack or fracture the formations,thereby increasing their permeability, is a relatively new method whichhas met with commercial success in certain types of formations such asthe Sprayberry sand found in certain areas in West Texas. Theeffectiveness of formation fracturing is limited by the capacity of thepumping equipment and bythe tendency of the high pressure injectionfluid to follow the open channels of least resistance instead of openingup new channels.

The present invention is directed toward an improved method ofincreasing the permeability of oil producing formations by firstinjecting into the formation a liquid explosive which is sufficientlyshock-insensitive to withstand injection pressures as high as 10,000p.s.i., or higher, and well temperatures up to 350 F., or higher, andsecond, detonating the liquid explosive in situ in the formation.

It has been found that a liquid explosive having the I The sensitizednitromethane is relatively shock insensitive and is not easily detonatedby accidental means. A.2 kg. Weight dropped 15 cm. resulting in animpact force of 30 kg. cm. will detonate nitroglycerine, whereas a- 4kg. weight dropped cm. resulting in an impact force of 500 kg. cm.failed to detonate sensitized nitromethane. A pressure increase on theorder of 35,000 lbs. per second is necessary to cause detonation atatmospheric temperatures. At higher temperatures a lesser rate ofpressure increase may cause detonation. No detonation was caused byslowly increasing the pressure from zero p.s.i. gage to 10,000 p.s.i.gage while maintaining a temperature of 350 F. The sensitizednitromethane was subsequently successfully detonated under theseconditions of high pressure and high temperature.

The sensitized nitromethane has a specific gravity of approximately1,139 and weighs 71.25 lbs per cu. ft. Its boiling point is 101.9 C.(215.4 F.) It is only slightly soluble in water (9.5%), while thesolubility of water in nitromethane is only 2.2%. These solubilitieshold true for salt water (3% sodium chloride) as Well as fresh water.

The sensitized nitromethane is not visibly miscible with crude petroleumoils. If agitated it will form a suspension which will settle out uponstanding for a few minutes.

Sensitized nitromethane, when detonated, has a velocity which iscomparable to other high explosives, such as nitroglycerine or TNT(trinitro-toluene). On the other hand,-the force exerted by sensitizednitromethane when detonated is considerably greater than that ofunsensitized nitromethane, and is comparable with other high explosivessuch as nitroglycerine or TNT.

Sensitized nitromethane is stable at normal ambient temperatures andpressures. Its sensitivity to shock remains substantially unchanged bystorage in black iron drums, tin cans, or glass jars for periods of atleast on year and probably much longer.

. Freezing of sensitized nitromethane decreases its shock sensitivity,but upon melting, the shock sensitivity of the material is substantiallythe same as it was before freez- Sensitized nitromethane can betransported with safety but since it is a simple matter to sensitize it,this can usually be done at the job. Thus the transportation may involveno explosive material but only two.

slightly inflammable materials, for which the usual precautions shouldbe observed.

Sensitized nitromethane is not toxic when placed in contact with humanskin, and produces no permanent injurious eifects.

The products of combustion are principally carbon monoxide, carbondioxide and water.

Having described the nature and characteristics of the liquid explosive,the following description is given for its use for fracturing oil wellformations as illustrated in the drawings, wherein,

Fig. l is a vertical cross section of an oil well during the step: ofpumpingthe liquid explosive into the bore;

ofthe well;

Fig. 2' shows the, well of Fig. 1 during the step offorcing, the liquidexplosive into the oil-producing formation.

Fig. 3 shows the well of Figs. 1 and 2' with the detonator in place,ready to be fired.

Figs. 4 and 5 show an alternative arrangement of the method shown. inFigs. 1 to 3 wherein the bore; of-

embodiment. of a pumping method for injecting liquid explosive into awell formation and detonating the explosive in situ. place-as indicatedat.2: with its lower end above-the oil producing formation 3 which isshown as being atthe lower end: of the well. extends. from the top ofthe well to a point. near the. bottom ofthev well.

monlycalled a stinger.

pump truck having a high pressure pump 9 driven; by an-engine 10 andhaving a liquid storage tank 11.to receive liquid explosive.

Ifthe nitromethane hasbeen sensitized previously it istaken from thetank 11 by the pump 9 and forced through the tubing- 4 to the bottom ofthe well as indicated at 5. Since the sensitized nitromethane is heavierthan oil or water it will displaceany such Well fluids 13 upwardlyuntil-the top surface 14 of theliquid' explosive-is raisedto theapproximate top of the formation to be fractured. The tubing 4 is thenraised until the packer 6* is within the lower end of the well casing-1,as shown-in Fig. 2. The packer 6 maybe of any well known type,expandable either mechanically or by appliedhydraulicpressure, to sealoif the lowersecti'on" of-thewell from the-upper section thereof. A;liquidof less specific gravitythan-the liquid explosive and nonmiscibletherewith (such aspetroleum oil) is pumped downwardly through the tubing4-until most of the liquid explosive has beenforced into the pores,cracksand It is well" fissures -15; of the-oil producing formation.known thatif'a sufficiently high injection pressure is applied, theoverburden can be lifted and the formation can.

be cracked, usually along bedding planes.- Such methods'are usuallyreferred to ashydraulic formation fracturing. The-effectiveness of suchhydraulic formation fracturing methods is limited to a relatively smallarea surrounding the bore of well and in many instances is whollyineffective in increasing the area of the drainage-channels leading fromthe oil producing formation to the bore of the well.

After-the liquid explosive. has been forced .into the. oil

producing formation, while leaving'thebore hole full of liquid.explosive. 5, as shown in Fig. 2, the packer 6 is collapsed andiswithdrawn from the well alo,ng--with the tubing 4. If the wellpressures are balanced the. fluid-interfaced?between the,liquidexplosive 5 and the well fluid 13 will remain-stationary, as shownin'Fig. 3.

Various meanszcanbe ,used to. detonate. the explosive liquid: 5. Fig 3illustrates, one suchmeanscomprising A well casing 1 is shown cementedin',

A string of oil well; tubing 4" An expandable packer 6 is attachedtto.the lower end of thetubing 4. Below the packer and; attached thereto .isa length of perforated pipe 7, com-.. The upper end of the tubing. 4 isconnected to the discharge line 8' of a conventional:

n electric,v wire, line hoist truck 18 having. an insulated. conductorcable 19 on the lower end of which is a detonator or series ofdetonators 20 which are immersed in the liquid explosive 5 in the boreof the well throughout the formation which is to be fractured. When theelectric circuit is closed by the operator of the truck 18 thedetonators 20 are fired, thereby detonating the liquid explosive 5 not.only in thewell borebut also laterally into the pores, cracks. andfissures 15 in the. formation." The resulting. explosion tends to form.new" cracks and fi'ssuresand to connect up existing; cracks, andfissures so that the drainage area in communication with the Wellbore'is greatly increased, thus permitting-an increase in the rate offlow of oil from the formation into the bore of the well.

An explosion once initiated in a body of sensitized nitromethane tendsto travel throughout the body of liquidand-' throughout these pores,cracks andfissures which contain a continuous body of liquidexplosive.The-foree -exertedby the explosion is very 'great-"and' issuffici'envtoenlarge the pores, cracks and-fissures for as great a distance from theboreof' the well as the liquidexplosive has-traveled while'maintaining acontinuous liquid phase.

If it is desired" tosensitize' the nitromethane at-the well, -sothatitis-not necessary to transport sensitized nitrometh'ane-tothewell, thiscan be.- done by injecting the sensitizerintothe nitromethane in thetank 11 (Fig! l)=-or; preferably', into the streamr'of nitromethanedischargedlfg'ydhe-pump/9.- In the latter case a'liquid injeetor'ZZj-fe'd-from a-suppl y tank 23, is interposed in thepipe-8leading-from-thepump-9 to thetubing 4 A- by-pass' 24 can beprovided'around= the injector '22, -if-' desired.

lfthe boreof thewell is of-large diameter or if thethicknessofthe-formation-tobe fractured-is very great it may notbedesirablet'ohave the entire bore hole throughout theproducingformation filled with explosive; particularly since such explosive isnot veryeffective iii-increasingthe'areaof the pores, cracks andfissuresat adistancefrom-the bore-hole. In this event the stinger 7'a'(-Fig. 4) below the packer 6 can be made of a f1"angible m'aterial; suchas aluminum, magnesium or the like;- and-=ca-nbe made longenou'ghtoextend'substantially1 throughout the -zone-to=be fractured. After thetubing 4, packer-6and stinger 7:: have been runintotheawell and beforethe packer 6 has been expanded; the=well bore surroundingthestinger 7acan be-fil led with small pieces of sol-idmaterial, suchasmarbles 2S;whichdis place a-large portion 'of-the liquid explosive which wouldotherwise-fill-the bore of the well. After the/explosivehas beend'etonated-the tail pipe 7a will have been' dis-:- integrated alongwith-partof the marbles- 25: Th'e*=.resi due can beleftin the-Well tofunction as' a; grayelipaclc; or it can be removed by bailing ordrilling.

A sim-ilarlresult couldtbe obtained by making the stinger 7 a with alarge diameter, practicallyifilling the bore hole.:- except forv runningclearance, and fillingvthe 'interiorisofi the stin'ger' with marbles 'orthe like. (not shown)".

If'th'eloilI producing formations of the well: are very: porous andiifthere is insufiicientwell pressure'to'main: tainaa istaticzfiuid-ilevelat the top. of the producing format-.- tion; the.purnping'1nethod shownin .Figs.: 1 :to'3 ica'nrnot': be used. Inthis event the desired resultcamb'et obg tained by 'plaeing arupturablediaphragm 27I (Fig: 6-) at thedischarge end of the stinger 7b secured ins-place by the'di'scharge-nozzle'28; The well -tubingcan'iberun intothe well-dry andsubsequently filled wit-hexplosiveliquid'fronr the top of the well.Thedisc 27 cambe'mup tured'as indicated in Fig. 7 either by theweight'of'the liquidiinthe wellttub'ing or by applied pump pressure;allo'wingthe liquidexplosive to drain intothe well. A- detonator 29 canbe placed on top of the column of liquidexplmive. and can be detonatedwhen, the topjof the column of explosive reaches the top of the stinger7b. Detonation can be initiated by means of a pressure increase, a timebomb or by an electric detonator.

Still another method of performing the present process is illustrated inFigs. 8 and 9 wherein the liquid explosive 13a is lowered into the well30 in a dump bailer 31 on the lower end of an insulated electric cable32 attached to a hoist (not shown) at the top of the Well. Above thedump bailer 31 and attached thereto is a steel or other metal cylinder34, perforated as indicated at 35 and serving as a combustion chamber 36for a grain of solid propellant 37. An igniter 38 at the top of thepropellant grain 37 is connected to the leads 39 from the electric cable32. Surrounding the perforated cylinder 34 and covering the perforations35 is a heavy walled rub ber sleeve 41, fastened at both ends by clamprings 4-2. The propellant grain 37 is supported on a disc 43 having oneor more perforations 44 therethrough serving as outlets for the gasgenerated in the combustion chamber 36. The lower end of the dump bailer31 is provided with discharge ports 46 which are normally closed bysuitable means such as a rupturable disc 47. If desired, a movable plug(or free floating piston) 50 can be placed on top of the liquidexplosive 13a to protect it from contact with the heat or flame from theburning propellant 37.

When the electric circuit through the insulated line 32 is closed by theoperator at the top of the Well the igniter 38 is ignited and, in turn,ignites the upper end of the propellant grain 37.

The propellant grain 37 is preferably an end-burning grain coated with asuitable restriction 48 on the sides and bottom thereof to preventburning except from the top down, as indicated in Fig. 9. The outsidediameter of the propellant grain 37 is preferably made somewhat smallerthan the inside diameter of the combustion chamber 36 so that gasesgenerated by the burning of the propellant from its upper end can traveldownwardly around the propellant grain and out through the perforations44 in the supporting disc 43.

Owing to the confinement of the hot gases in combustion chamber 36 bythe imperforate diaphragm 47 a pressure is build up within thecombustion chamber 36, bailer 31 and sleeve 41 with the result that thesleeve 41 is first expanded tightly against the wall 49 of the well boreor well casing, as shown in Fig. 9. As the pressure continues to buildup, the diaphragm 47 is ruptured and the liquid explosive is forced intothe bore hole and into the formation by the expanded packer 41 whichprevents the liquid explosive from migrating up the bore hole and theexplosive is thereby forced into the formation.

When the propellant 37 has been completely burned, the temperaturewithin the combustion chamber and dump bailer drops from a high of15003500 F. to normal well temperature of 100-350 F. with a resultantpressure decrease, permitting the packer 41 to collapse so that the toolcan be withdrawn from the well.

Following this operation a detonator such as is illustrated in Fig. 3 islowered into the well, into the body 6 of liquid explosive remaining inthe bore of the Well and is detonated.

The term solid propellant, as used herein, means any of the so-calledslow-burning solid propellants such as are commonly used in rockets orjet assistance take-off units for airplanes. The term slow-burning asused herein means that the burning rate, for an end-burning grain, is onthe order of .05" per second at pressures up to approximately 1,000 psi.

The term sensitized nitromethane, as used herein, meansmononitromethane, either pure or commercial grade, to which has beenadded a small percentage of an amine or mixture of amines sufiicientlybasic to form salts with a weak acid, as hereinabove set forth. Thepercentage of sensitizer can be varied in any practical amount butsatisfactory results are obtained with two to three percent, by volume,of nitromethane.

The term sensitized as used herein, means that the shock sensitivity ofthe nitromethane has been increased to such a degree that thenitromethane can be detonated readily by means of common, high velocity,detonators such as Primacord, either pentaerythritoltetranitrate orcyclotiimethylenetrinitramine.

While the foregoing specification and drawings illustrate threedifierent methods of performing the invention herein described, it is tobe understood that the invention is not necessarily limited to thesethree embodiments but is of the scope defined by the appended claims.

I claim:

1. A method of increasing the productivity of a formation penetrated bya well comprising the steps of introducing into the well a liquidexplosive comprising sensitized nitromethane, causing said sensitizednitromethane to enter the pores, cracks and fissures in said formationand detonating said sensitized nitromethane in situ in said formation.

2. A method as defined in claim 1 in which pressure is applied to thesensitized nitromethane after it has been introduced intothe well toforce said sensitized nitromethane into the formation.

3. A method as defined in claim 1 in which mononitromethane issensitized with an organic amine.

4. A method as defined in claim 1 in which mononitromethane issensitized with diethylamine.

5. A method as defined in claim 1 in which mononitromethane issensitized with aniline.

6. A method as defined in claim 1 in which mononitromethane issensitized with morpholine.

7. A method as defined in claim 1 in which mononitromethane issensitized with an aliphatic amine.

8. A method as defined in claim 1 in which mononitromethane issensitized by a mixture of amines selected from the group consisting ofdiethylamine, aniline and morpholine.

References Cited in the file of this patent UNITED STATES PATENTS

1. A METHOD OF INCREASING THE PRODUCTIVITY OF A FORMATION PENETRATED BYA WELL COMPRISING THE STEPS OF INTRODUCING INTO THE WELL A LIQUIDEXPLOSIVE COMPRISING SENSITIZED NITROMETHANE, CAUSING SAID SENSITIZEDNITROMETHANE TO ENTER THE PORES, CRACKS AND FISSURES IN SAID FORMATIONAND DETONATING SAID SENSITIZED NITROMETHANE IN SITU IN SAID FORMATION.